Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
123 PM EST Sat Dec 13 2025

Valid 12Z Tue Dec 16 2025 - 12Z Sat Dec 20 2025


...Multiple atmospheric rivers will impact the Pacific Northwest
next week...

...Overview...

Upper pattern will transition to a strongly zonal/quasi-zonal flow
over the CONUS with embedded shortwaves over much of next week.
This suggests below average confidence in system timing with
changeable conditions over many areas. Influx of Pacific moisture
will come in waves to the Pacific Northwest, yielding additional
modest to perhaps heavier rainfall and mountain snow. Some of this
rainfall may cause flooding concerns given the recent heavy
rainfall over the region. Temperatures will be milder than normal
for most of the Lower 48. Additional rainfall is likely to expand
from the Midwest/Mid-South to the East Coast later in the week.


...Guidance/Predictability Assessment...

With the fast flow, model/ensemble spread is higher than normal
and confidence in timing is lower than normal. But, the 00/06Z
guidance was relatively well-clustered through the period. The 06Z
GFS was a bit slower with a Canadian low pressure around Thursday
but within the spread. By next Saturday, the Canadian was on the
slower side of the ensemble spread like the ECMWF-AIFS, but the
ECMWF AIFS-ENS was close to its dynamical counterpart. Thus, a
blend of the latest models/ensembles served as a good starting
point for the surface progs given a lack of meaningful signal
otherwise.

Fracasso

...Weather/Hazards Highlights...

Into Tuesday, another atmospheric river is likely to be taking aim
at the Northwest. The core of the IVT will be oriented toward
northern California for the longest duration, which has not seen as
much rain in recent days as Washington/Oregon and is thus not as
sensitive to heavy rain. Meanwhile a couple rounds of more
transient IVT are expected farther north into the Pacific
Northwest. This region has much more sensitive antecedent
conditions, but a colder regime compared to the recent event will
mean more of the precipitation falls as snow across much of the
Cascades. Additionally, this moisture plume should be oriented more
southwesterly rather than completely orthogonal to terrain. A
Marginal Risk is in place for Day 4/Tuesday ERO stretching across
northern California into the Pacific Northwest. Continue to monitor
if a Slight Risk is needed, but given limiting factors for
flooding in both regions, will continue to hold off. Wednesday
should see a relative break in QPF overall. However, some lingering
rain is forecast in the Pacific Northwest and could lead to
isolated flooding concerns given the sensitivity. Thus a low end
Marginal Risk is in place for Day 5/Wednesday for northwest Oregon
into western Washington. Yet another AR seems likely to impact the
Northwest by Thursday, which could be strong, so additional
flooding will be a concern. The IVT plume is likely to drift
gradually south toward northern California on Friday.

As impulses move out of the Northwest across the northern tier,
rain and snow could spread across the northern Plains late Tuesday
into Wednesday and into the Midwest and Great Lakes region
Wednesday-Thursday. Farther south, some Gulf moisture return is
possible for light to moderate rain across eastern Texas into the
Lower and Middle Mississippi Valley for Tuesday and Wednesday. By
Thursday these systems are likely to interact and spread broadening
precipitation chances across the eastern third of the U.S. Most of
this precipitation is likely to be rain except in the Great Lakes
to interior Northeast. Most precipitation should be pulling away on
Friday, but with some lake effect precipitation possible behind
the main system and in advance of the next High Plains front.

Colder than average temperatures are likely to persist into
Tuesday across eastern portions of the country, but with lesser
anomalies than the cold short range period. Low temperatures in the
20s are still expected for the Southeast though, 10-20 degrees
below average. Meanwhile, warmer than average conditions are
forecast for most of the West into the Plains where scattered
record highs are possible. These warmer than average temperatures
should gradually expand eastward, reaching the East on Thursday for
a warmer than average period, until another cold front passes for
late week. The highest anomalies will likely be across the High
Plains most days, as highs in the 60s expand into western Nebraska
and South Dakota. By Saturday, temperatures in much of Texas could
reach 80F.


Tate


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw